Spring covers for jamb liners of non-take-out windows occupy only the upper half of the sash run. Platforms engaging the lower corners of a sash are then free to move up and down in the lower half of each jamb liner, where no spring covers occur. The requirement for half-length spring covers in these systems is more expensive than extruding or forming the jamb liners as a single piece with a full-length spring cover.
There have been some suggestions for full-length spring covers enclosing block and tackle balance systems from which a cord runs outside the spring cover to engage a sash. None of these have been in commercial use, so far as applicants are aware. The Wood U.S. Pat. No. 4,134,234 is an example of this, and Wood suggests a block and tackle balance extending for the full length of the jamb liner, with the cord passing from the top of the jamb liner downward through a long open slot in a check rail region of the jamb liner. Dinsmore U.S. Pat. No. 3,358,403 and Osten U.S. Pat. No. 2,774,119 suggest other arrangements of block and tackle balances deploying cords or tapes that extend through a spring cover to engage a sash.
We have improved on such systems by devising a guide that guides a cord through the spring cover so as to provide load-related friction helping to prevent hop and drop of the balanced sash. Our guide also closes the necessary opening in the spring cover, helps anchor the balance system within the spring cover, helps anchor the balance system with the spring cover, and helps deploy a platform where it will automatically engage a sash assembled into position between a pair of jamb liners. Our improvement also includes better supports attachable to a free end of the cord for engaging the bottom of a balanced sash. All these improvements aim at economy, efficiency, durability, reliability, and weather sealing.